Reinforcing material for wood and reinforced wood

ABSTRACT

A phenol resin-impregnated sheet formed by impregnating a porous resin sheet with a phenol resin having a degree of cure of from 70% to 95% is arranged on and lamininated to the surface of a carbon fiber-reinforced thermosetting resin sheet. The thickness of the phenol resin impregnated sheet is between 0.01 mm and 1.0 mm. A very even, strong and water-proof wood reinforcing material is obtained. The wood reinforcing material is intergrated and cured on the surface of the wood material by the phenol resin-impregnated sheet to reinforce wood material (single board or bonded board) to form a reinforced wood material. The wood reinforcing material adheres suitably with the wood material and does not cause environmental contamination.

FIELD OF THE INVENTION

This invention relates a wood reinforcing material for strengtheningwood material and a reinforced wood material reinforced with the woodreinforcing material.

BACKGROUND OF THE INVENTION

Heretofore, single wood materials or so-called bonded wood materialsformed by bonding sawn woods or small square lumbers cut longitudinallyin the direction of fibers with the direction of the fibers being inparallel with each other have been used mainly as frame materials suchas post and beams in buildings, as well as for wooden bridges or largescale domes.

Particularly, since the bonded wood materials are assembled from sawnwoods and small square lumbers, they have excellent characteristics suchas high degree of freedom for the size and dimension, less variation inthe strength of products, cracks or errors cause by drying, as well ascapable of easily manufacturing bent materials.

However, when such bonded wood materials are used for large buildingsand structures, since the rigidity and strength of the bonded materialshave to be increased, it is necessary to increase the thickness for thebonded materials and, as a result, this causes problems such as loweringof ceilings in the buildings and structures, or.unnecessary increase inthe height of roofs.

Therefore, for providing the bonded wood materials and single woodmaterials with high rigidity and strength and also providing sufficientwater proofness, corrosion resistance, fire resistance, heat resistanceand adhesion required for the buildings or structures of woods, it hasbeen proposed to bond carbon fibers by adhesives such as phenolic resinsor resorcinolic resins to obtain reinforced wood materials such ascarbon fiber-reinforced single wood materials or carbon fiber-reinforcedbonded wood materials.

As one of methods for manufacturing such reinforced wood materials,Japanese Laid-Open No. 230904/1991, for instance, discloses a method ofcoating an adhesive on the surface of wood material, disposing carbonfibers thereon and impregnating an adhesive between the fibers and alsobonding the same with the wood material (Prior Art 1).

As another method of manufacturing the carbon fiber-reinforced singlewood material or carbon fiber-reinforced bonded wood material, JapanesePatent Laid-Open No. 108182/1978 proposes a method of using a so-calledprepreg in which an adhesive is previously impregnated sufficiently tocarbon fibers and bonding the same to a wood material (Prior Art 2).This method enables working in various places and is suitable also inview of the fabricability and, accordingly, has been used generally.

The present inventors have proposed a wood reinforcing material bybonding a wood reinforcing carbon fiber prepreg and a wooden sheet inJapanese Patent Laid-Open No. 254319/1997 (Prior Art 3). In this citedinvention, release paper is not necessary, the resultant woodreinforcing material has high strength and high rigidity and can obtainhigh stable properties regarding adhesion performance between the woodensheet and the wood material, or adhesion performance between the woodensheet and carbon fibers.

In the Prior Arts 1 and 2, since the wood material is natural productshaving different natures depending on the growing environments, itinvolves a problem that adhesion fluctuates when the carbon fiberprepreg and the wood material are bonded. Further, for ensuring thebondability, it requires a frequent control for selecting and optimizingthe state such as solid, semi-solid or liquid and amount thereof, whichleaves various problems with view point of cost performance and quality.

In the Prior Art 2 described above, since carbon fiber prepregs aregenerally transported or stored being rolled or stacked into sheets, sothat release paper is disposed on one surface or both surfaces of theprepreg. However, when bonding with the wood materials, troublesome andtime consuming fabrication operations are necessary such as for removalof the release paper, as well as removed release paper yields wastes andthe use of prepregs have resulted in environmental contamination.

In the Prior Art 3 described above, the wooden sheet itself causes shearfailure in the bending failure test and sufficient reinforcing effectcan not always be obtained.

The present inventors have intended to provide a wood reinforcingmaterial which is applied to wood materials or bonded wood materials forreinforcement capable of overcoming the problems in the prior art, aswell as a reinforced wood material in which the wood reinforcingmaterial is applied to the surface of the wood material or to the innerlayer of the bonded wood material.

Specifically, this invention intends to provide a wood reinforcingmaterial excellent in bondability with the wood material andhandlability, not causing environmental contamination such as formingwastes of release paper, and having a sufficient reinforcing effect forthe wood material, as well as reinforced wood material.

More specifically, this invention intends to provide a wood reinforcingmaterial of reducing fluctuation of adhesion performance, strength andrigidity caused by variation in wood materials as natural products andminimizing the complexity in view of the working and minimizing thewastes, as well as having high bondability, strength and rigidity, aswell as a reinforced wood material applied with the wood reinforcingmaterial.

SUMMARY OF THE INVENTION

It is an object of the present invention to solve the foregoingproblems.

In accordance with a wood reinforcing material of this invention, aphenol resin-impregnated sheet with a degree of cure of 70% or more and95% or less in which a porous sheet is impregnated with a phenol resinis disposed on the surface of a carbon fiber-reinforced thermosettingresin sheet.

Further, in accordance with a reinforced wood material of the invention,the wood reinforcing material is integrated and cured by way of a phenolresin-impregnated sheet on the surface of a wood material.

In the wood reinforcing material of the invention, since a phenolicresin-impregnated sheet with a degree of cure of 70% or more and 95% orless is disposed, it forms a molding product showing excellent adhesionto a wood material to be reinforced and also free from stickiness, sothat it does not require release paper. Accordingly, the reinforced woodmaterial according to this invention which is reinforced by applying thewood reinforcing material of the invention to the surface of the woodmaterial has a feature of high strength, high rigidity and high shearstrength.

Carbon Fiber-reinforced Thermosetting Resin Sheet

A carbon fiber-reinforced thermosetting resin sheet as a constituentfactor of the wood reinforcing material of this invention is reinforcedwith carbon fiber in the thermosetting resin as reinforcing fibers.

There is no particular restriction on the carbon fibers and carbonfibers obtained from polyacrylonitrile fibers with a nitrogen content of0.1 to 15% by weight, a tensile strength of 2,500 to 7,000 MPa and amodulus of elasticity of 150-700 GPa are preferred and, particularly,carbon fibers of 5 to 9 mm diameter containing 3 to 10% of a nitrogencontent and having 3,500 MPa or more of tensile strength and 200 to 350GPa of modulus of elasticity are preferred in view of the adhesion.

Further, those in which the oxygen/carbon ratio of 0.01/1 to 0.3/1,particularly, 0.01/1 to 0.25/1 at the surface of the carbon fibers ofthis invention by an ESCA surface analyzer (manufactured by ShimazuSeisakusho) are preferred since the adhesion strength can be improved.

It is desired that carbon fibers with the fiber diameter of from 5 to 9mm and fiber strands comprising the fibers by the number of 1,000 to300,000 are used by being bundled or spread in a sheet-like shape in anamount, with no particular restriction only thereto.

The form of the carbon fiber may be a multi-directional sheet such aswoven or non-woven fabrics or linear materials such as uni-directionallyoriented sheets or rovings.

Kinds of the thermosetting resins reinforced with carbon fibers have noparticular restrictions and, in view of use for buildings, one or moremember selected from isocyanate type resins or resorsinol resins, orresol type phenolic resins are preferred, formaldehydes are preferred asthe curing agent for the thermosetting resin and inorganic acids ororganic acids are preferred for curing catalysts.

Referring more specifically to the thermosetting resins, known resoltype phenol resins (phenol formaldehyde initial polycondensation resins)and resorcinol resins obtained by methyloling phenols having a phenolhydroxy group such as phenol, cresol, xylenol, ethylphenol, chlorophenoland bromophenol or phenols having two or more phenolic hydroxy groupssuch as oligomer, and resorcin, hydroquinone, catechol andfluoroglycinol, and aldehydes such as formaldehyde, para-formaldehyde,acetoaldehyde, fulfural, benzaldehyde, trioxane and tetraoxane, at amolar ratio of phenols/aldehydes=2/1 to 1/3, preferably, 5/4 to 2/5,under the presence of an alkali catalyst such as potassium hydroxide orsodium hydroxide can be used.

More preferably, resins having an average molecular weight aspolystyrene of 120 to 2000, and, particularly, 150 to 500 according tohigh speed liquid chromatography (HPLC) are preferred and those resinshaving viscosity adjusted to 3 to 150 poise at 25-C are preferred.

Among known curing agents used for resorcinol resins and resol typephenol resins curing agents which become paste or liquid when mixed withthe resins such as formaldehyde, acetoaldehyde, furfural or trioxane arepreferred.

Curing catalysts which are dissolved into liquid form when mixed withresins such as para-toluene sulfonic acid, benzene sulfonic acid, xylenesulfonic acid and phenol sulfonic acid are preferred.

In view of the production process of the carbon fiber-reinforcedthermosetting resin sheets, curing agents or curing catalysts which formhomogeneous liquid at 35-C or lower as a temperature for usualproduction of prepregs when prepared as mixed resins for uniformlycuring the prepregs are preferred.

In the fiber reinforcing material of this invention, the carbonfiber-reinforced thermosetting resin sheet as a constituent factor maybe a prepreg sheet or a completely cured sheet. It is preferred that thesheet is completely cured with an aim of increasing the strength of thecarbon fiber-strengthened resin composite material per se.

Phenol Resin-impregnated Sheet

The phenol resin impregnated sheet as a constituent factor of the woodreinforcing material of this invention is a sheet formed by impregnatinga porous sheet with a phenol resin, for improving the adhesion strengthwhen the wood reinforcing material is bonded by an adhesive on thesurface of wood material. Accordingly, it is important that the sheethas thin and uniform thickness.

The thickness of the phenol resin-impregnated sheet is preferably 0.01mm or more and 1.0 mm or less. If the thickness is less than 0.01 mm,the sheet performance is deteriorated by unevenness caused to the formof the phenol resin-impregnated sheet and, depending on the case,curling in the lateral direction and, in addition, the strength of thesheet is lowered to allow easy tearing by an external force or result indifficulty in the handlability. On the other hand, if the thickness ismore than 1.0 mm, the water proofness or shear strength is sometimeslowered.

The porous sheet can include, regarding the form, for example, non-wovenfabric, paper and wooden fabric and can include, regarding material, forexample, pulp, glass fiber and carbon fiber and synthetic fiber.

The resin impregnating in the phenol resin-impregnated sheet used inthis invention is a highly viscous or solid resin such as a phenolicresin or phenol/melamine resin mixture, with no restriction for thepresence or absence of the curing agent, and use of a less reactiveresin capable of controlling the degree of cure is preferred forattaining the purpose of this invention.

The phenol resin is used because this is excellent in fire proof andheat resistant performance and, further, excellent in water proofness,corrosion resistance and bondability and, thus, this can be usedsuitably to building materials.

Actual examples of such phenol resins are phenols having one phenolichydroxy group such as phenol, cresol, xylenol, ethylphenol, chlorophenoland bromophenol or phenols having two or more phenolic hydroxy groupssuch as oligomer and resorcine, hydroquinone, catechol andfluoroglycinol and, further, resins formed by mixing one or more ofresins such as melamine, epoxy, and unsaturated esters with the resinsmentioned above.

In the wood reinforcing material of this invention, it is preferred thatthe degree of cure of the phenol resin in the phenol resin-impregnatedsheet as the constituent factor is controlled to 70% or more and 95% orless, preferably, 75% or more and 90% or less, in order to keepfavorable adhesion and shear strength. That is, if the degree of thecure of the resin is less than 70%, peeling occurs in the phenolresin-impregnated sheet because of the low degree of the cure of thephenol resin and, on the other hand, if it exceeds 95%, curing proceedsexcessively and reactivity with the adhesive is lowered to result inpeeling at the boundary with the wood material.

Further, when the degree of cure of the resin in the phenolresin-impregnated sheet is controlled to 70% or more and 95% or less,the wood reinforcing material of this invention forms a molding productwith no stickiness thus making it unnecessary for the use of releasepaper which is indispensable for usual prepregs during storage ortransportation.

The degree of cure is measured as follows.

{circle around (1)} For identical phenol resin-impregnated sheets, anuncured phenol resin-impregnated sheet and an optionally cured phenolresin-impregnated sheet are dried each by 100 cm² in a desiccatorcontaining a silica gel at a normal temperature for 30 min. under areduced pressure and then further dried in a pressure reduced state for15 hrs. The weight for the uncured phenol resin-impregnated sheet andthe optionally cured phenol resin-impregnated sheet in this case isdefined as WO, WO′, respectively.

{circle around (2)} Each of the uncured phenol resin-impregnated sheetand the optionally cured phenol resin-impregnated sheet in above {circlearound (1)} is extracted for five hours with the solvent for the phenolresin-impregnated sheet such as acetone using a Soxhlet extractor, driedin a desiccator containing silica gel at a normal temperature for 2hours under a reduced pressure and, further, dried for 15 hrs in apressure reduced state. The weight for the uncured phenolresin-impregnated sheet and the optionally cured phenolresin-impregnated sheet in this case is defined as W1, W1′,respectively.

{circle around (3)} Degree of cure is calculated based on and describedabove {circle around (1)} and {circle around (2)} in accordance with thefollowing equation 1.

Degree of cure (%)=(1−( W0′−S1′)/(W0−W1))×100  formula (1)

Composite Structure of Wood Reinforcing Material

The carbon fiber-reinforced thermosetting resin sheet and the phenolresin-impregnated sheet can take the following composite structures (1)and (2).

Composite Structure (1):

A composite structure in which the carbon fiber reinforced thermosettingresin sheet and the phenol resin-impregnated sheet are entirely bondedand integrated.

Composite Structure (2):

A composite structure in which the carbon fiber-reinforced thermosettingresin sheet and the phenol resin-impregnated sheet are point-bonded andintegrated.

Such composite structures (1) and (2) can be obtained by the followingmanufacturing method.

Manufacturing Method:

A phenol resin-impregnated sheet is appended on one surface or bothsurfaces of a so-called prepreg sheet formed by impregnating carbonfibers with a thermosetting resin for wood reinforcement, and thenintegrating them by using a hot press or the like such that the degreeof cure of the phenol resin-impregnated sheet is 70% or more and 95% orless. The thermosetting resin for the carbon fibers in this case may notalways be cured completely.

Reinforced Wood Material

The reinforced wood material in this invention can include single woodmaterials or bonded wood materials and there are no particularrestrictions so long as they are existent wood materials and, usually,wood materials used for building such as cedar, hinoki cypress, larch,Pseudotsuga taxifolia Britt and peel of Citrus aurantium and woodmaterial used for plywoods such as Japanese oak, paulownia, zelkova,maple, horse chestnut, Magnolia obovata Thumb, cherry, teak, lauan andSPINAL can be used.

Reinforcement of Wood Material

Wood reinforcing material of this invention (carbon fiber reinforcedresin composite material) is used for wood reinforcement as shown below.

The wood reinforcing material of this invention is appended on thesurface of a single wood material or to the surface of the single boardor any one of board, or between single boards or the surface of a bondedmaterial comprising a plurality of boards or single board and integratedand cured into a reinforced wood material, optionally, with theinterposition of adhesives or further necessary, under heating and underpressure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an example of a wood reinforcing material of thisinvention which is shown being decomposed on every constituent factors.In FIG. 1, in the wood reinforcing material (carbon fiber-reinforcedresin composite material) of this invention, a phenol resin-impregnatedsheet 1 is disposed on both surfaces of a carbon fiber-reinforcedthermosetting resin sheet 2.

FIG. 2 illustrates an example of a wood reinforcing material of thisinvention which is shown being decomposed on every constituent factors.In the reinforced wood material in FIG. 2, a wood reinforcing material 4of this invention is disposed for reinforcement on both surfaces of asingle wood material 3. Although not shown particularly in FIG. 2, anadhesive resin is usually present between the single wood material 3 andthe wood reinforcing material 4.

FIG. 3 is a cross sectional view for an example of a reinforced woodmaterial in which bonded material is reinforced by using the woodreinforcing material of this invention. In the reinforced wood materialin FIG. 3, a wood reinforcing material 4 comprising a plurality oflayers is disposed on a bonded material 5 laminated in a plurality oflayers and, further, a single wood material 3 is disposed on the woodreinforcing material 4. Although not particularly illustrated in FIG. 3,an adhesive layer is usually interposed between the single wood material3 and the wood reinforcing material 4, between the wood reinforcingmaterial 4 and the wood reinforcing material 4, between the woodreinforcing material 4 and the bonded material 5 or between the bondedmaterial 5 and the BONDED material 5.

DETAILED DESCRIPTION OF THE INVENTION

The wood reinforcing material of this invention will described morespecifically with reference to the accompanying drawings.

The wood reinforcing material of this invention can be manufactured, forexample, as shown below.

It is manufactured by dipping strands of carbon fibers continuously in aliquid resin mixture formed by mixing one or more of thermosettingresins, a curing agent or a curing catalyst and, optionally, aninorganic filler such that the resin mixture is 30 to 80% by weightbased on the carbon fibers, drying evaporative contents, if necessary,then winding the fibers so as to be in parallel with each other on aphenol resin-impregnated sheet previously wound around a drum, dryingoptionally and cutting the same in the lateral direction of the drum, ormanufactured by a method of impregnating a resin into fibers whilearranging carbon fiber strands on a phenol resin-impregnated sheet inwhich the resin is previously coated while pressing by a roll on thesurface in parallel with each other.

It is preferred that the resin mixture is a homogeneous solution foruniformly impregnating the carbon fibers and conducting curinguniformly. If it is not uniform, the resultant carbon fiber-reinforcedthermosetting resin sheet (prepreg) causes curing failure, or theadhesion is lowered, which is not preferred.

Further, when the amount of the resin mixture of the carbonfiber-reinforced thermosetting resin sheet impregnated with the resinmixture is 30% by weight or less, not only the strength property is notdeveloped but also the bondability with the phenol resin-impregnatedsheet is poor because of the insufficiency of the amount of the resin.On the other hand, when the amount of the resin mixture in the carbonfiber-reinforced thermosetting resin sheet is more than 80% by weight,the strength property is not developed which that the carbon fibers aredisturbed being caused by the resin flow during molding, as well asdifficulty is caused to the handlability such as drop of the resin fromthe carbon fiber-reinforced thermosetting resin sheet because ofexcessive amount, which is not preferred.

Particularly, it is preferred when the amount of the resin mixture inthe carbon fiber-reinforced thermosetting resin sheet is from 40 to 60%by weight, since the strength property, bondability with the phenolresin-impregnated sheet or handlability of the carbon fiber-reinforcedthermosetting resin sheet are favorable.

Further, the viscosity of the resin mixture at 25-C is preferably from 3to 150 poise. If the viscosity is 3 poise or less, the resin tends todrop from the prepreg and, on the other hand, if it is 150 poise ormore, impregnation of the resin into the carbon fibers is deteriorated,which is not preferred.

The viscosity can be controlled with addition of water or alcohol.

The wood reinforcing material of this invention can be manufactured byappending a phenol resin-impregnated sheet to a carbon fiber-reinforcedthermosetting resin sheet, pressurizing them and, optionally, heatingthem into integration. The degree of cure of the phenolresin-impregnated sheet in this case is controlled 70% or more and 95%or less, which may be controlled by heating for once or heating fortwice or more during preparation, or by culture at normal temperature.

The wood reinforcing material of this invention and a single woodmaterial and a bonded wood material are bonded and integrated as shownbelow.

That is, an existent wood adhesive, if necessary, the resin formed bymixing the resin and an inorganic acid or an organic acid as a curingagent or curing catalyst used in this invention, a resin mixture usedfor the carbon fiber prepreg can be coated to the surface of the singlewood material or the bonded wood material, and the surface of the thinboard of the bonded wood. After coating the resin to the wood surface,the wood reinforcing material is appended such that the direction of thecarbon fibers is parallel with the fiber direction of the wood and, in acase where the reinforced wood material is a thin board for bonded woodmaterial, the wood reinforcing material and other several thin boardsfor bonded wood material are laminated by way of an adhesive by a knownmethod and then heated under a pressure of 1 to 15 kg/cm² at atemperature of normal temperature to 120-C for 5 to 24 hours to obtainthe reinforced wood of this invention.

This invention is to be explained concretely by way of examples but theinvention is not restricted to the following examples unless it exceedsthe scope thereof.

The viscosity of the resin for use in the carbon fiber resin compositematerial was measured and determined by using a rheology physicalproperty tester (manufactured by Rheology Co.).

Further, bending test and bondability test (cole test, boiled test andblock shearing test) for wood material, bonded wood material and carbonfiber reinforced wood material and bonded wood material thereof wereconducted in accordance with Agricultural and Forest Standards of Japanfor structural bonded wood material. The cold test and the boiled testwere conducted in application circumstance 1.

EXAMPLE 1

Strands of carbon fibers “BESFITE (registered trade name) HTA12K”(manufactured by Toho Rayon Co.) having fiber characteristics of asingle fiber diameter of 7 mm, total number of fibers of 12,000, atensile strength of 3,890 MPa and a tensile modulus of elasticity of 236GPa were passed through a resin bath containing a resin mixture obtainedby uniformly mixing and dissolving 82 parts of resol type phenol resin“AH-343” (manufactured by Lignite Co.) having a viscosity at 20-C of 35poise and 18 parts of an organic curing agent mainly comprisingpara-toluene sulfonic acid “D-5” (manufactured by Lignite Co.) by 5mm/min, at a room temperature and for a dip time of 0.5 min., and woundaround a drum of 127 cm diameter to a width of 100 cm such that thestrands were in parallel while controlling by a squeeze roll such thatthe resin content was 55% by weight to form a carbon fiber-reinforcedthermosetting resin sheet of 100 cm width and about 4.0 m length, withthe total carbon fiber weight of 150 g/M².

After cutting the carbon fiber-reinforced thermosetting resin sheet to arectangular shape of 100 mm width and 250 mm length and laminating themby two layers, a phenol resin-impregnated sheet of 0.25 mm thickness(trade name of products: phenol resin-impregnated sheet PFP2,manufactured by Lignite Co.) was appended on both surfaces and heatcured to be integrated under a pressure of 5 kg/cm² at a temperature of100-C for a retention time of 3 hrs to form a flat board of a woodreinforcing material of this Example 1 (a carbon fiber reinforced resincomposite material). The carbon fiber content in the wood reinforcingmaterial is 50% by volume and the degree of cure for the phenolresin-impregnated sheet is 80%.

A single cedar board of 60 mm width, 75 mm length and 10 mm thicknesswas bonded to both surfaces of the flat board of the wood reinforcingmaterial of 60 mm width and 75 mm length cut out of the flat woodreinforcing material by using a resin formed by mixing 85 parts ofresorcinol resin D300 (trade name) and 15 parts of para-formaldehydeH30M (trade name), the curing agent therefor manufactured by OhkashinkoCo., to prepare the reinforced wood material of this Example 1.

Cold test, boiled test and block shearing test were conducted for thethus obtained reinforced wood material as the specimen.

Further, in the same manner as in the method described above,rectangular flat boards of wood reinforcing material of 30 mm width, 500mm length and 45 mm width and 2 m length were prepared in the samemanner as described above. They were bonded to a cedar board of 30 mmwidth, 500 mm length and 25 mm thickness and a bonded wood materialformed by laminating four cedar layers each of 45 mm width, 2 m lengthand 25 mm thickness respectively using the resin consists of theabove-mentioned D300 and H30M and bending strength was measured.

The results are shown in the following Table 1. The reinforced woodmaterial formed by integrating the wood reinforcing material of Example1 and the wood material had excellent adhesion performance and strengthcharacteristic capable of satisfying Agriculture and Forestry Standardof Japan.

COMPARATIVE EXAMPLE 1

A wood reinforcing material (FRP) was prepared in the same manner as inExample 1 by using the carbon fiber-reinforced thermosetting resin sheetmanufactured in the same manner as in Example 1 except for laminatingthe sheet by two layers and not appending the phenol resin-impregnatedsheet thereto. This was bonded and integrated with the wood material(cedar) in the same manner as in Example 1 to obtain a reinforced woodmaterial of Comparative Example 1, to which adhesion test and bendingtest were conducted. The results are shown in the following Table 1.This did not satisfy the adhesion test according to Agriculture andForestry Standards of Japan and the bending strength showed nosatisfactory value although improved somewhat.

COMPARATIVE EXAMPLE 2

A wood reinforcing material was prepared by using the carbonfiber-reinforced thermosetting resin sheet prepared in the same manneras in Example 1 except for laminating the sheet by two layers andappending a wooden sheet (spruce) instead of the phenolresin-impregnated sheet. This was bonded and integrated with the woodmaterial (cedar) in the same manner as in Example 1 to prepare areinforced wood material, to which adhesion test and bending test wereconducted. The results are shown in the following Table 1. Although thissatisfied the adhesion test according to Agriculture and ForestryStandards of Japan but shear fracture was caused in the spruce in thebending test and no sufficient value was obtained for the improvement ofthe bending strength.

TABLE 1 Comparetive Comparative Item Not-reinforced Example 1 Example 1Example 2 Molding material Surface material None Phenol resin- FRP sheetSpruce sheet impregnated sheet Thickness — 0.25 mm — 0.45 mm Degree ofcure — 80% — — Material in FRP None CF/phenol CF/phenol CF/phenol Formof fiber None Umidirectional Umidirectional Umidirectional CF amount 2 mbending test None 300 g/m² × 4 300 g/m² × 4 300 g/m² × 4 layer layerlayer Other test None 150 g/m² × 2 150 g/m² × 2 150 g/m² × 2 layer layerlayer Bonded material Cedar Cedar Cedar Cedar Adhesive Phenol resinPhenol resin Phenol resin Phenol resin Boiled test Delamination (%) 1st0 0 32 0 2nd 0 0 69 0 Main Delamination form None None Between wood Nonesheet Cold test Delamination (%) 1st 0 0 15 0 2nd 0 0 26 0 MainDelamination form None None Between wood None sheet Block shearing testShear strength 98 kgf/cm² 112 kgf/cm² 92 kgf/cm² 102 kfg/cm² Woodfailure 100% 88% 46% 5% rate Failure form Wood broken Wood brokenBetween wood Spruce shear sheet 50 cm bending test Bending strength 742kgf/cm² 1430 kgf/cm² 1270 kgf/cm² 1230 kgf/cm² Failure form Wood brokenWood broken Between wood Spruce shear sheet 2 m bend test Bendingstrength 283 kgf/cm² 763 kgf/cm² 442 kgf/cm² 397 kgf/cm² Failure formWood broken Wood broken Between wood Spruce shear sheet

EXAMPLE 2

A test specimen was prepared in the same manner as in Example 1 exceptfor changing the fabrication temperature to 90-C upon manufacture of thewood reinforcing material in Example 1, and adhesion test was conducted.The results are shown in the following Table 2.

The degree of cure of the phenol resin-impregnated sheet of the woodreinforcing material in Example 2 was 75%, which showed adhesionperformance satisfying the Agriculture and Forestry Standards of Japan.

EXAMPLE 3

A test specimen was prepared in the same manner as in Example 1 exceptfor changing the fabrication temperature to 110-C upon manufacture ofthe wood reinforcing material in Example 1, and an adhesion test wasconducted. The results are shown in the following Table 2.

The degree of cure of the phenol resin-impregnated sheet of the woodreinforcing material in Example 3 was 90%, which showed adhesionperformance satisfying the Agriculture and Forestry Standards of Japan.

Comparative Example 3

A test specimen was prepared in the same manner as in Example 1 exceptfor changing the fabrication temperature to 80-C upon manufacture of thecarbon fiber-reinforced thermosetting resin sheet in Example 1, andadhesion test was conducted. The results are shown in the followingTable 2.

The degree of cure of the phenol resin-impregnated sheet of the woodreinforcing material in Comparative Example 3 was 50%, which showedadhesion performance not satisfying the Agriculture and ForestryStandards of Japan.

COMPARATIVE EXAMPLE 4

A test specimen was prepared in the same manner as in Example 1 exceptfor changing the fabrication temperature to 150-C upon manufacture ofthe carbon fiber-reinforced thermosetting resin sheet in Example 1, andan adhesion test was conducted. The results are shown in the followingTable 2.

The degree of cure of the phenol resin-impregnated sheet of the woodreinforcing material in Comparative Example 4 was 99% or more, whichshowed adhesion performance not satisfying the Agriculture and ForestryStandards of Japan.

TABLE 2 Comparative Comparative Item Example 2 Example 3 Example 3Example 4 Molding material Surface material Material Phenol resin-Phenol resin- Phenol resin- Phenol resin- impregnated impregnatedimpregnated impregnated sheet sheet sheet sheet Thickness 0.25 mm 0.25mm 0.25 mm 0.25 mm Degree of cure 75% 90% 50% 99% FRP sheet MaterialCF/phenol CF/phenol CF/phenol CF/phenol CF form UnidirectionalUnidirectional Unidirectional Unidirectional Bonded material Cedar CedarCedar Cedar Wood sheet adhesive Phenol resin Phenol resin Phenol resinPhenol resin Boiled test Delamination (%) 1^(st) 0 0 5 100 2^(nd) 0 0 7100 Delamination form None None In impregnated Between wood sheet sheetsCold test Delamination (%) 1^(st) 0 0 0 15 2^(nd) 0 0 3 32 Delaminationform None None In impregnated Between wood sheet material Block shearingtest Shear strength 110 kgf/cm² 109 kgf/cm² 95 kgf/cm² 64 kgf/cm²Failure form Wood broken Wood broken In impregnated Between wood sheet

Industrial Applicability

Since the wood reinforcing material of this invention is formed bydisposing a phenol resin-impregnated sheet with a degree of cure of 70%or more and 95% or less on the surface of the carbon fiber-reinforcedthermosetting resin sheet, it can solve the problem of wastes caused byrelease paper resulted in existent carbon fiber prepregs and hasexcellent bondability to wood materials.

Since the reinforced wood manufactured by using the wood reinforcingmaterial of this invention has high strength, particularly, highstrength in a bending failure test and high adhesion and rigidity, andhas sufficient water proofness, corrosion resistance, fire proofness,heat resistance and long time stability, wood materials and bondedmaterials reduced in the weight and increased in the size can bemanufactured efficiently.

The reinforced wood material (reinforced single wood material and bondedwood material) of this invention are applicable to application uses inwhich they are used as usual wood materials and bonded wood materialsand, in particular, they are suitable as aggregates for large buildingssuch as schools, gymnasiums, assembly houses, various kinds of indoorball game stadia and domes, three or more storied residences andaggregates for wooden bridges. Further, even wood materials not usableso far because of low strength of low rigidity can be employed, whichcan lead to effective utilization of various resources and are useful inview of environmental preservation.

Furthermore, this can extend the application uses of wood materials tolarge scale buildings and structures not possible so far, as well as canreduce the amount of natural wood materials used.

The reinforced wood material of this invention can reduce thefluctuation of adhesion performance, strength and rigidity caused byscatterings present in wood materials as natural products.

What is claimed is:
 1. A wood reinforcing material, comprising: a carbonfiber-reinforced thermosetting resin sheet; and a phenolresin-impregnated sheet arranged on a surface of said carbonfiber-reinforced thermosetting resin sheet, said phenolresin-impregnated sheet being formed by impregnating a porous sheet witha phenolic resin having a degree of cure of from 70% to 95% according toSoxhlet extraction.
 2. A wood reinforcing material as claimed in claim1, wherein the degree of cure of said phenol resin-impregnated sheet isfrom 75% to 90%.
 3. A wood reinforcing material as claimed in claim 1,wherein the thickness of said phenol resin-impregnated sheet is from0.01 mm to 1.0 mm.
 4. A wood reinforcing material as claimed in claim 1,wherein a matrix resin of said carbon fiber-reinforced thermosettingresin sheet is cured and bonded and integrated with said phenolresin-impregnated sheet.
 5. A wood reinforcing material as claimed inclaim 1, wherein a matrix resin of said carbon fiber-reinforcedthermosetting resin sheet is a phenol resin.
 6. A reinforced woodmaterial in which the wood reinforcing material as claimed in claim 1 isintegrated and cured on the surface of a material to be reinforced byway of said phenol resin-impregnated sheet.
 7. A reinforced woodmaterial as claimed in claim 6, wherein the wood material to bereinforced is a single wood material or a bonded wood material.